Conventional apparati for cleaning objects with solvent, for example for degreasing of metal objects, normally contain an upwardly open vessel in which a layer of solvent vapour is maintained. Objects to be cleaned are immersed in the vapour, and the vapour condenses on the object and runs down into the lower portion of the vessel. The bottom region of the vessel is often made as a boiling container for the solvent, with thermostats and cooling means being arranged to assure a suitable vapour level in the vessel.
To reduce loss of vapour out into the atmosphere surrounding the vessel, suction gaps can be arranged at the edge of the vessel to remove solvent-contaminated air for purification.
Apparati of said type can be said to have three operating states, namely a first operating state where the solvent vapour is kept at the intended level in the vessel so that the apparatus is ready for treatment of an object, a second operating state where the solvent is kept warm but with the solvent vapour at a low level so that the apparatus can be made operative relatively quickly, and a third state where the apparatus is shut off, for example on weekends, at night or during lunch.
The last-mentioned state results in losses of solvent due to evaporation. Such loss is undesirable both for economic and environmental reasons, since solvent is relatively costly and national regulations can limit permissible discharge from the apparatus.